In today's rapidly advancing semiconductor manufacturing industry, device feature sizes continue to shrink as integration levels increase. Several barriers are being encountered in the attempt to shrink device feature sizes of VLSI (Very Large Scale Integration) devices below the 100 nm range. This is true for both FEOL (front end of line) and BEOL (back end of line) processes. One of the device features that must be reduced in size in order to accommodate VLSI devices in the 100 nanometer range, are the trenches, vias, or contacts formed through dielectric layers and that are filled with conductive interconnect material and which contact underlying conductive features. Such openings are typically formed using plasma etching operations. The plasma etching operation usually creates residue in the opening and it is difficult to remove the residue. As the size of the opening is reduced, it becomes more difficult to remove the residue and the unremoved residue obstructs a larger part of the smaller opening. It would therefore be desirable to provide a method that effectively removes residue from very small openings and allows for good contact to be made to the underlying contact layer when a conductive material is formed in the opening.
Supercritical fluids have been used to clean semiconductor wafers. Supercritical fluid extraction is the name given to a cleaning process that removes contaminants using a supercritical fluid, that is, a gas-like substance above its critical temperature and pressure. Supercritical fluids are fluids at a temperature above which pressure cannot be used to liquefy the fluid. A wafer cleaning system in process using supercritical fluids is disclosed in “Supercritical Fluids For Single Wafer Cleaning”, Bok, et al, Solid State Technology, June, 1992, the contents of which are herein incorporated by reference. Supercritical fluids have been found to be effective in cleaning contamination from bare wafers. It would therefore be desirable to use supercritical fluids to clean residue from openings formed through dielectric layers and in conjunction with a subsequent deposition process that forms a barrier layer on the cleaned surfaces of openings, particularly small openings in the less than 100 nanometer range.